Hydraulic power units normally comprise a prime mover, for example, an electric motor, gasoline or diesel engine, a pump, fluid tank, control valves, cooler, filters, etc.
The prime mover/pump assembly requires special shaft alignment and shimming and is usually built upon a machined base, which is mounted on, under, or beside the fluid tank. In prior art systems, the fluid tank is normally sized so that its fluid volume is three times the pump flow rate. As a result, such known tanks are large and expensive and require two to three times the floor space that the prime mover/pump assembly alone requires.